Radio receiver



March 3, 1936. L, Q WALLER 2,@32,675

RADIO RECEIVER Filed NOV. 18, 1933 INVENTOR ZZZ/W0 C. MALE/F ATTORN EY Patented Mar. 3, 1936 v 7 k UNITED STATES PATENT OFFICE RADIO RECEIVER Leland C. Waller, Arlington, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application November 18, 1933, Serial No. 698,594 Claims. (01. 250-2'0) An object of my invention is to increase the heterodyne frequency by avariable condenser l2. selectivity of that class of radio receivers which By this arrangement, the coupling between the are used for the reception of modulated waves. oscillator plate and control grid is chiefly by Another object is to decrease the background means of the electron stream within the tube.

. noise of the usual type of tuned radio receiver. The magnitude of the local oscillator voltage 5 A still further object of the invention is to inimpressed on the grid of tube 6 may be regulated crease the gain and sensitivity of the usual type to the desired amount by means of a variable of superheterodyne receiver. By using two difresistor l3 series connected with condenser l4 ferent intermediate frequencies and amplifying between the oscillator plate and ground. The

; the signal at each of these frequencies 1 find primary coil l5 in the plate circuit of tube 6 is 10 that a very high total amplification may be secoupled to a secondary 5 connected in the grid cured and at the same time the tendency toward circuit of an intermediate frequency amplifier oscillation is reduced to substantially zero or IT. Coils l5 and It may be adjustably tuned by eliminated. variable condensers l8 and 19 to the same pri- Another object is to reduce the image signal maryintermediatefrequencyof, say, 465 kilocycles. 15 response in a superheterodyne type of receiver The plate circuit of tube I1 is coupled to the by utilizing a relatively high first or primary. grid circuit of a second frequency converter 20 intermediate frequency. The voltage gain that by a primary coil 2| and secondary coil 22, these is sacrificed by the use of a high primary intercoils also being tuned to 465 kilocycles by variable 20 mediate frequency is compensated for by the condensers'23 and 24. A coil in the plate cir- 20 secondary intermediate frequency amplifier. cuit of a-vacuum tube oscillator 26 is also in- A still further object of the invention is to ductively coupled to coil 22 to impress the heteroprovide a superheterodyne receiver using two dyne oscillations generated by tube 26 on the intermediate frequencies and in which the first grid of tube 2|]. The magnitude of the oscillations 25 local oscillator is of the electron coupled type and so impressed may be controlled by the series con- 25 the second is of the crystal-controlled type gennection of variable resistor 21 and condenser 28 crating a very constant frequency current. connected as shown. The oscillations generated Other objects of the invention will be apparent by tube 26 are maintained at a very constant to those skilled in the art as the description frequency by means of a quartz or other known thereof proceeds. The novel features which I type of piezo-electric crystal 29 connected as 30 believe to be characteristic .of my invention are shown in the control grid circuit of the oscillator. set forth in particularity in the appended claims,. I prefer to make crystal 29 of such a size that the invention itself, however, as to both its organthe oscillations generated by tube 26 have a freization and method of operation will best be quency of-290 or 640 kilocycles, either of which understood by reference to the following descripform a beat frequency of 175 kilocycles with the 35 tion taken in connection with the drawing in primary intermediate frequency of 465 kilocycles. which the single figure is a diagrammatic circuit I term the 1'75 kilocycle frequency the secondary diagram of an arrangement whereby my invenintermediate frequency. As shown, the screen tion may be carried into effect. grid circuit of tube 26 which may be an R. C. A.

Referring to the drawing, the modulated radio 24A type is tuned by coil 30 and condenser 3| 40 frequency signal waves picked up by antenna toenable'the triode portion of tube 26 consisting I may be impressed on grid circuit 2 of a radio of the cathode, control grid and screen grid to frequency amplifier 3, circuit 2 being tunable oscillate at the crystal frequency, the plate or to the signal frequency by means of variable conoutput circuit of the tube being chiefly electron denser 4. The output circuit of amplifier 3 is coupled to the oscillatory circuit. With this ar- 45 coupled to the coil 5 in the grid circuit of the rangement' the fundamental frequency of the first frequency converter or detector 6, the grid oscillator issubstantially unaffected by a change circuit being tuned to the incoming signal freof the impedance of its plate circuit, so that quency by variable condenser 'l. A coil 8 in the variation of resistor 21 or other changes in the plate circuit of a local oscillator 9 is also inducplate circuit will produce relatively small fre- 50 tively coupled to coil 5. Oscillator 9 may comquency variations. It will be understood that prise an R. C. A. 24A type tube and a feedback my invention is not limited to the use of the connection may be provided between the screen particular oscillator circuits or tube types shown grid l0 and its control grid H as shown, its control in either the first or second oscillator on the grid circuit being tunable to the desired local diagram, or to only two intermediate frequencies. 55

More than two intermediate frequencies can be used if desired, with an additional crystal-controlled oscillator for each new intermediate frequency used. Any practical type of oscillator tube or circuit may be used for both the first and second oscillator positions.

The plate circuit of tube 20 is shown coupled to the grid circuit of an intermediate frequency amplifier 32 by primary coil 33 and secondary coil 34, these coils being tuned to 175 kilo'cycles by adjustable condensers 35 and 36. The plate circuit of tube 32 is shown coupled to the grid circuit of another stage of intermediate fre quency amplification 31 by means of primary coil 38 and secondary coil 39, these coils being tuned to 175 kilocycles by adjustable condensers 40 and 4|.

The signal modulations in the plate circuit 01'. tube 37 may be detected and amplified in any preferred manner. The means shown comprises a secondary coil coupled to a primary coil 44, these being tuned to 175 kilocycles by condensers 41 and 46 respectively. As shown the ends of coil 45 are connected to the plates 43 of a double or full wave rectifier and audio amplifier tube 42 which may be of the type known as R. G. A. 55, the detected audio signals being impressed on the grid 48 of the triode amplifier portion of the tube by condenser 49. The output of tube 42 may be further amplified by a pair of power amplifier tubes 50 connected in push-pull as "shown. Any desired type of sound reproducer maybe connected to the output circuit of tubes 50, that shown being a loudspeaker 5| coupled to the plate circuit of the tubes by a transformer 52-.

Suitable voltages are supplied to thelseveral tubes by a tapped resistor 53 the end terminals 54 of which may be connected across the output terminals of a 300 volt battery 55 or of a rectifier (not shown). The condenser 12 may be designed to produce a constant beat frequency with the incoming signal frequency in a known manner, the uni-control operating means diagrammatically indicated by numeral 56 then serving to adjust it along with tuning condensers 4 and 1. The output volume of the set may be adjusted to the desired value by adjustable contact arm 51 which serves to control the bias of the grids connected thereto.

I have found that by use of a crystal oscillator 7 such as that shown, the selectivity of the receiver is increased substantially above that obtained when the usual vacuum tubeoscillator is used and which is subject to frequency variation or drift for different reasons. This is due to the exceedingly sharp resonance peak characteristic of the crystal oscillator, inasmuch as the se1ec tivity of two tuned circuits is in general proportionalto the product of the selectivity of each. The use of the crystal oscillator also is found to cause the background noise in the receiver to be considerably less than that obtained with the usual superheterodyne receiver.

Also, while I have used 465 and kilocycles as primary and secondary intermediate frequencies it will be understood that my invention is not limited to the use of these particular frequencies but other frequencies may be used instead. I have found, however, that by using intermediate frequency amplifiers operating at two substantially difierent frequencies a very highdegree of gain may be secured without theamplifier going into oscillation which is difficult or impossible to prevent when a number-of high gain tuned amplifiers are all operating at the same frequency. By the use of two intermediate frequencies which differ by a substantial amount, the tendency toward oscillation of the amplifiers is substantially eliminated. I have also found that the use of a relatively high frequency, in the neighborhood of 500 kilocycles, as the primary intermediate frequency, reduces the image signal response of the receiver.

The receiver described may be used to receive modulated radio frequency signals having frequencies within the present broadcast band or signals in the high frequency band having wavelengths of the order of as low as 5 meters by using tubes, coils and tuning condensers having proper characteristics; Also if the sharp resonance peak of the crystal oscillator causes too great an attenuation of the side bands of the carrier, such effect may be compensated for by overcoupling the coupling coils 33, 34 and 38, 39 0f the secondary intermediate frequency stages so as to secure a double peaked resonance curve, or by any known method of selective audio-frequency amplification. Furthermore, the receiver can be used in conjunction with a local heterodyne oscillator in a known manner for the reception of continuous-wave modulated or unmodulated telegraph signals.

Having described my invention what I desire to secure by Letters Patent is:

1. A superheterodyne receiver comprising, a Vacuum tube detector having a grid circuit and a .plate circuit, means for impressing modulated signal oscillations on said grid circuit, a vacuum tube oscillator having a plate circuit coupled to said grid circuit and "said oscillator having a tunable control grid circuit and a screen grid circuit with a feedback connection to said tunable grid circuit arranged to generate oscillations whose frequency difi'ers from said signal oscillations by a primary intermediate frequency, means for amplifyingsaid intermediate frequency oscillations, a "second detector having a grid circuit coupled to said last namedamplifying means, a crystal controlled oscillator arranged to generate oscillations of a constant frequency differing from the primary intermediate frequency by a secondary intermediate frequency which is substantially lower than said primary frequency, means for impressing the oscillations generated by said crystal oscillator on the grid circuit of said second detector, means for amplifying said secondary intermediate frequency oscillations, and means for detecting said last named amplified oscillations.

2. The combination defined in the preceding claim in which said crystal controlled oscillator output circuit is provided with the series conapplied to the grid circuit of the second detector.

3. A superheterodyne receiver comprising in combination, a vacuum tube detector having a grid circuit and a plate circuit, means for impressing modulated signal oscillations'onsaid grid circuit, a vacuum tube oscillator having a grid circuit tuned to a frequency differing from said signal oscillations by a primary intermediate frequency, and a plate circuit coupled to said tuned grid circuit by electron coupling only, means coupling said plate circuit to the grid circuit of said detector, a variable resistor and condenser connected in series between the plate and cathode of said oscillator for controlling the oscillation voltage impressed on said detector grid circuit, amplifying means coupled to the plate circuit of said detector for amplifying said primary intermediate frequency oscillations, a second detector having a grid circuit coupled to said amplifying means, a crystal controlled oscillator arranged to generate oscillations of constant frequency differing from said primary intermediate frequency by a secondary intermediate frequency which is less than half the value of said primary frequency, means for impressing the oscillations from said crystal controlled oscillator on a grid circuit of said second detector and for controlling the voltage of said impressed oscillations, means coupled to the output circut of said second detector for amplifying said secondary intermediate frequency oscillations, means for rectifying said amplified oscillations, and means for indicating said rectified oscillations.

4. A superheterodyne receiver comprising the combination of a vacuum tube detector having a grid circuit and a plate circuit, means for impressing modulated signal oscillations on said grid circuit, a vacuum tube oscillator having a control grid circuit tuned to a frequency differing from said signal oscillations by a primary intermediate frequency, a screen grid circuit and a plate circuit, a feedback coupling between said screen grid and said control grid circuits, means coupling said plate circuit to the grid circuit of said detector, amplifying means coupled to the plate circuit of said detector for amplifying said primary intermediate frequency oscillations, a second detector having a grid circ t coupled to said amplifying means, a vacuum tube oscillator having a control grid circuit, a screen grid circuit and a plate circuit, means for tuning said screen grid circuit to a frequency differing from said primary intermediate frequency by a secondary intermediate frequency which is substantially lower than said primary intermediate frequency, a piezo electric crystal connected to the control grid circuit of said oscillator, means coupling the plate circuit of said oscillator to the grid circuit of said second detector, means coupled tothe output circuit of said second detector for amplifying said secondary intermediate frequency oscillations, means for rectifying said amplified oscillations and means for indicating said rectified oscillations.

5. The combination defined in claim 4 in which the plate and control grid circuits of each of said oscillators are coupled by electron coupling only.

LELAND C. WALLER. 

